Is this possible?
And if, how? There seems to be no JTAG?
It is possible but difficult to debug without JTAG. You will need to Buy a domino and ask us to send you a blank one or you can send us yours and we will erase it for you.
Hmm,
I will buy a Panda instead of sending my Domnio from Germany to you 
I wanted to add the possibility for setting up some kind of software interrupt to run a high priority task.
Note that FEZopen project is “in progress” but it is open source with community collaboration. It is not a plug-and-play thing like our standard firmware.
Would it be possible that GHI add such a feature to the Domino? “software interrupt to run a high priority task.”
You mean this http://www.tinyclr.com/forum/1/1503/
Note that not everything you are trying to accomplish can be done with NETMF, even if you were to write the port yourself.
NETMF is the greatest thing to happen to embedded computing but there are places (small areas) where NETMF is not well suited. An example is when having some very tight timing requirements. For those needs, even a PC will not do the job, you need a small little micro programmed in C or better in assembly.
So, what are you trying to do? I will make it easier for you and tell you if this can or can’t be done 